Intravascular stent with inverted end rings

ABSTRACT

The invention is directed to an expandable stent for implanting in a body lumen, such as a coronary artery, peripheral artery, or other body lumen. The invention provides for an intravascular stent having a plurality of cylindrical rings connected by undulating links. A plurality of inverted cylindrical end rings can be coupled at least in part to a plurality of adjacent cylindrical rings in the form of mirror images such that a symmetrical configuration is present on at least one of a proximal end and a distal end of the stent. The stent has a high degree of flexibility in the longitudinal direction, yet has adequate vessel wall coverage and radial strength sufficient to hold open an artery or other body lumen. The inverted end ring configuration of the stent aims at reducing the stent-to-shoulder distance as well as delivering therapeutic drug to the peri-stent area while maintaining a pristine stent deployment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of co-pending U.S. Ser. No. 11/751,506filed May 21, 2007, which is a division of U.S. Ser. No. 10/631,159filed Jul. 12, 2004, now abandoned, the contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to vascular repair devices, and in particularintravascular stents, which are adapted to be implanted into a patient'sbody lumen, such as a blood vessel or coronary artery, to maintain thepatency thereof. Stents are particularly useful in the treatment ofatherosclerotic stenosis in arteries and blood vessels.

Stents are generally tubular-shaped devices which function to hold opena segment of a blood vessel or other body lumen such as a coronaryartery. They also are suitable for use to support and hold back adissected arterial lining that can occlude the fluid passageway. Atpresent, there are numerous commercial stents being marketed throughoutthe world. For example, the prior art stents depicted in FIGS. 1-3 havemultiplex cylindrical rings connected by one or more undulating links.While some of these stents are flexible and have the appropriate radialrigidity needed to hold open a vessel or artery, there typically is atradeoff between flexibility and radial strength and the ability totightly compress or crimp the stent onto a catheter so that it does notmove relative to the catheter or dislodge prematurely prior tocontrolled implantation in a vessel.

What has been needed and heretofore unavailable is a stent which has ahigh degree of flexibility so that it can be advanced through tortuouspassageways and can be readily expanded, and yet have the mechanicalstrength to hold open the body lumen or artery into which it isimplanted and provide adequate vessel wall coverage. In particular, itwould be desirable to have a stent with an end ring configuration thataims at reducing the stent-to-shoulder distance as well as deliveringtherapeutic drug to the peri-stent area while maintaining a pristinestent deployment. The present invention satisfies these and other needs.That is, the stent of the present invention has a high degree ofcompressibility to secure it on the catheter and provide a low profileand a high degree of flexibility making it possible to advance the stenteasily through tortuous arteries, yet the stent has sufficient radialrigidity so that it can hold open an artery or other blood vessel, ortack up a dissected lining and provide adequate vessel wall coverage.

SUMMARY OF THE INVENTION

The present invention is directed to an intravascular stent that has aninverted cylindrical end ring configuration incorporated into the stentpattern on at least one of a proximal end and a distal end of the stent,which helps in reducing the stent-to-shoulder distance as well asdelivering therapeutic drug to the peri-stent area while maintaining apristine stent deployment. The stent also is highly flexible along itslongitudinal axis to facilitate delivery through tortuous body lumens,but which is stiff and stable enough radially in its expanded conditionto maintain the patency of a body lumen such as an artery when the stentis implanted therein.

The stent of the present invention generally includes a plurality ofcylindrical rings, including a plurality of inverted cylindrical endrings at each stent end, which are interconnected to form the stent. Thestent typically is mounted on a balloon catheter if it is balloonexpandable or mounted on or in a catheter without a balloon if it isself-expanding.

Each of the cylindrical rings making up the stent have a proximal endand a distal end and a cylindrical plane defined by a cylindrical outerwall surface that extends circumferentially between the proximal end andthe distal end of the cylindrical ring. Generally the cylindrical ringshave a serpentine or undulating shape which includes at least oneU-shaped element, and typically each ring has more than one U-shapedelement. The cylindrical rings are interconnected by at least oneundulating link which attaches one cylindrical ring to an adjacentcylindrical ring. The undulating links are highly flexible and allow thestent to be highly flexible along its longitudinal axis.

The undulating links may take various configurations but in general havean undulating or serpentine shape. The undulating links can includebends connected by substantially straight portions wherein thesubstantially straight portions are substantially perpendicular to thestent longitudinal axis.

Not only do the undulating links that interconnect the cylindrical ringsprovide flexibility to the stent, but the positioning of the links alsoenhances the flexibility by allowing uniform flexibility when the stentis bent in any direction along its longitudinal axis. Uniformflexibility along the stent derives in part from the links of one ringbeing circumferentially offset from the links in an adjacent ring.Further, the cylindrical rings are configured to provide flexibility tothe stent in that portions of the rings can flex or bend and tipoutwardly as the stent is delivered through a tortuous vessel.

The cylindrical rings typically are formed of a plurality of peaks andvalleys, where the valleys of one cylindrical ring are circumferentiallyoffset from the valleys of an adjacent cylindrical ring. In thisconfiguration, at least one undulating link attaches each cylindricalring to an adjacent cylindrical ring so that at least a portion of theundulating links is positioned within one of the valleys and it attachesthe valley to an adjacent peak.

While the cylindrical rings and undulating links generally are notseparate structures, they have been conveniently referred to as ringsand links for ease of identification. Further, the cylindrical rings canbe thought of as comprising a series of U's, W's and Y-shaped structuresin a repeating pattern. Again, while the cylindrical rings are notdivided up or segmented into U's, W's and Y's, the pattern of thecylindrical rings resembles such configuration. The U's, W's and Y'spromote flexibility in the stent primarily by flexing and by tippingradially outwardly as the stent is delivered through a tortuous vessel.

In one embodiment, the stent includes a plurality of invertedcylindrical end rings coupled at least in part to a plurality ofadjacent cylindrical rings on at least one of a proximal end and adistal end of the stent. At least one inverted cylindrical end ring canbe a mirror image of at least one corresponding adjacent cylindricalring such that a symmetrical configuration is present on at least one ofthe proximal end and the distal end of the stent.

In a further embodiment, it is contemplated by the present inventionthat at least a portion of the stent may have a variable thicknessconfiguration. For example, the stent may include a combination of ringsand links having a variable thickness throughout the length of thestent. Alternatively, select struts of the inverted cylindrical endrings may have a variable thickness while the cylindrical rings andlinks maintain a standard thickness throughout the length of the stent.

In other embodiments, the inverted cylindrical end rings are shown incombination with various alternative stent patterns. It should beappreciated that the inverted cylindrical end rings of the presentinvention may be used with virtually any stent design and are not meantto be limited to the designs set forth herein. Accordingly, theresultant shape of the inverted cylindrical end rings will be dependenton the type of stent design used for a particular application. Forexample, if the cylindrical rings are all U-shaped then the invertedcylindrical end rings likewise can “mirror” that respective shape sothat complete symmetry exists on at least one of the proximal end andthe distal end of the stent. In yet another embodiment, the invertedcylindrical end rings may assume a different shape than thecorresponding adjacent cylindrical rings.

The number and location of undulating links that interconnect adjacentcylindrical rings can be varied as the application requires. Since theundulating links typically do not expand when the cylindrical rings ofthe stent expand radially outwardly, the links are free to continue toprovide flexibility and to also provide a scaffolding function to assistin holding open the artery. Importantly, the addition or removal of theundulating links has very little impact on the overall longitudinalflexibility of the stent. Each undulating link is configured so that itpromotes flexibility whereas some prior art connectors actually reduceflexibility of the stent.

The cylindrical rings of the stent are plastically deformed whenexpanded when the stent is made from a metal that is balloon expandable.Typically, the balloon-expandable stent is made from a stainless steelalloy or similar material.

Similarly, the cylindrical rings of the stent expand radially outwardlywhen the stent is formed from superelastic alloys, such asnickel-titanium (NiTi) alloys. In the case of superelastic alloys, thestent expands upon application of a temperature change or when a stressis relieved, as in the case of a pseudoelastic phase change.

Because of the undulating configuration of the links, the stent has ahigh degree of flexibility along the stent axis, which reduces thetendency of stent fishscaling. Stent fishscaling can occur when thestent is bent and portions of the stent project outward when the stentis in the unexpanded condition. The present invention stent withinverted cylindrical end rings reduces the likelihood of fishscaling.

Further, because of the positioning of the links, and the fact that thelinks do not expand or stretch when the stent is radially expanded, theoverall length of the stent is substantially the same in the unexpandedand expanded configurations. In other words, the stent will notsubstantially shorten upon expansion. The inverted cylindrical end ringsof the present invention likewise play a significant role in preventingthe substantial shortening of the stent upon expansion due to theability of the inverted cylindrical end rings to undergo completeexpansion when the stent is in an implanted diameter.

In all embodiments, the rings (including the inverted cylindrical endrings) and links may include reservoirs to retain therapeutic drugs. Thereservoirs may be formed as either micro-channels or micro-depots withinthe rings or links. The material of the rings or links associated withthese reservoirs may be either a polymer or a metal.

The stent may be formed from a tube by laser cutting the pattern ofcylindrical rings, inverted cylindrical end rings, and undulating links,directly in the tube. The stent also may be formed by laser cutting aflat metal sheet in the pattern of the cylindrical rings, invertedcylindrical end rings, and links, and then rolling the pattern into theshape of the tubular stent and providing a longitudinal weld to form thestent.

Other features and advantages of the present invention will become moreapparent from the following detailed description of the invention, whentaken in conjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially in section, of a prior artstent mounted on a rapid-exchange delivery catheter and positionedwithin an artery.

FIG. 2 is an elevational view, partially in section, similar to thatshown in FIG. 1 wherein the prior art stent is expanded within theartery, so that the stent embeds within the arterial wall.

FIG. 3 is an elevational view, partially in section, showing theexpanded prior art stent implanted within the artery after withdrawal ofthe rapid-exchange delivery catheter.

FIG. 4 is a photograph of a three-dimensional view of a prototype stenthaving inverted cylindrical end rings in a fully expanded diameter.

FIG. 5 is a photograph of a three-dimensional view of a stent withoutinverted cylindrical end rings in an expanded diameter.

FIG. 6A is a plan view of a flattened stent, which illustrates thepattern of the rings and links without the inverted end rings of thepresent invention.

FIG. 6B is a partial plan view of the stent of FIG. 6A, which has beenexpanded to approximately 3.0 mm inside diameter.

FIG. 6C is a plan view of a portion of the stent of FIG. 6A rolled intoa cylindrical configuration and tightly crimped so that the variousstent struts are either in close contact or contacting each other.

FIG. 7A is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the pattern of the rings and links,including the inverted end rings.

FIG. 7B is a partial plan view of the stent of FIG. 7A, which has beenexpanded to approximately 3.0 mm inside diameter.

FIG. 7C is a plan view of the stent of FIG. 7A, which is illustrated ina cylindrical configuration and is tightly crimped or compressed.

FIG. 7D is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the different patterns of the inverted endrings and the adjacent rings positioned at the proximal end of thestent.

FIG. 8A is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the pattern of the rings and links,including the inverted end rings.

FIG. 8B is a partial plan view of the stent of FIG. 8A, which has beenexpanded to approximately 4.0 mm inside diameter.

FIG. 8C is a plan view of the stent of FIG. 8A, which is illustrated ina cylindrical configuration and is tightly crimped or compressed.

FIG. 9A is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the pattern of the rings and links,including the inverted end rings.

FIG. 9B is a partial plan view of the stent of FIG. 9A, which has beenexpanded to approximately 4.0 mm inside diameter.

FIG. 9C is a plan view of the stent of FIG. 9A depicting the rings andlinks, including the inverted end rings, in a crimped or compressedconfiguration.

FIG. 10 is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the pattern of the rings and links,including the inverted end rings.

FIG. 11 is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the pattern of the rings and links,including the inverted end rings.

FIG. 12 is an enlarged partial perspective view of a portion of a peakand associated struts depicting variable thickness struts.

FIG. 13 is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the pattern of the rings and links,including the inverted end rings.

FIG. 14 is a plan view of a flattened stent of another embodiment of theinvention, which illustrates the pattern of the rings and links,including the inverted end rings.

FIG. 15 is an enlarged partial view of a flattened section of oneembodiment of the invention incorporating inverted cylindrical end ringsand adjacent cylindrical rings with micro-channels and micro-depots.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention stent improves on existing stents by providing alongitudinally flexible stent having a plurality of inverted cylindricalend rings coupled at least in part to a plurality of adjacentcylindrical rings that can be in the form of mirror images of oneanother such that a symmetrical configuration is present on at least oneof a proximal end and a distal end of the stent. In addition toproviding longitudinal flexibility, the stent of the present inventionalso provides radial rigidity and a high degree of scaffolding of avessel wall, such as a coronary artery. Further, the inverted end ringconfiguration of the present invention stent aims at reducing thestent-to-shoulder distance as well as delivering therapeutic drugs tothe peri-stent area while maintaining a pristine stent deployment.

Before describing in detail an exemplary embodiment of a stent inaccordance with the present invention, it is instructive to brieflydescribe a typical stent implantation procedure and the vascularconditions which are typically treated with stents. Referring now to thedrawings, FIG. 1 depicts a prior art stent 10 mounted on a conventionalcatheter assembly 12 which is used to deliver the stent and implant itin a body lumen, such as a coronary artery, peripheral artery, or othervessel or lumen within the body. The catheter assembly includes acatheter shaft 13 which has a proximal end 14 and a distal end 16. Thecatheter assembly is configured to advance through the patient'svascular system by advancing over a guide wire by any of the well knownmethods of an over the wire system (not shown) or a well known rapidexchange catheter system, such as the one shown in FIG. 1.

Catheter assembly 12 as depicted in FIG. 1 is of the well known rapidexchange type which includes an RX port 20 where the guide wire 18 willexit the catheter. The distal end of the guide wire 18 exits thecatheter distal end 16 so that the catheter advances along the guidewire on a section of the catheter between the RX port 20 and thecatheter distal end 16. As is known in the art, the guide wire lumenwhich receives the guide wire is sized for receiving various diameterguide wires to suit a particular application. The stent is mounted onthe expandable member 22 (balloon) and is crimped tightly thereon sothat the stent and expandable member present a low profile diameter fordelivery through the arteries.

As shown in FIG. 1, a partial cross-section of an artery 24 is shownwith a small amount of plaque that has been previously treated by anangioplasty or other repair procedure. Stent 10 is used to repair adiseased or damaged arterial wall which may include the plaque 26 asshown in FIG. 1, or a dissection, or a flap which are sometimes found inthe coronary arteries, peripheral arteries and other vessels.

In a typical procedure to implant stent 10, the guide wire 18 isadvanced through the patient's vascular system by well known methods sothat the distal end of the guide wire is advanced past the plaque ordiseased area 26. Prior to implanting the stent, the cardiologist maywish to perform an angioplasty procedure or other procedure (i.e.,atherectomy) in order to open the vessel and remodel the diseased area.Thereafter, the stent delivery catheter assembly 12 is advanced over theguide wire so that the stent is positioned in the target area. Theexpandable member or balloon 22 is inflated by well known means so thatit expands radially outwardly and in turn expands the stent radiallyoutwardly until the stent is apposed to the vessel wall. The expandablemember is then deflated and the catheter withdrawn from the patient'svascular system. The guide wire typically is left in the lumen forpost-dilatation procedures, if any, and subsequently is withdrawn fromthe patient's vascular system. As depicted in FIGS. 2 and 3, the balloonis fully inflated with the prior art stent expanded and pressed againstthe vessel wall, and in FIG. 3, the implanted stent remains in thevessel after the balloon has been deflated and the catheter assembly andguide wire have been withdrawn from the patient.

The prior art stent 10 serves to hold open the artery after the catheteris withdrawn, as illustrated by FIG. 3. Due to the formation of thestent from an elongated tubular member, the undulating components of thestent are relatively flat in transverse cross-section, so that when thestent is expanded, it is pressed into the wall of the artery and as aresult does not interfere with the blood flow through the artery. Thestent is pressed into the wall of the artery and will eventually becovered with endothelial cell growth, which further minimizes blood flowinterference. The undulating portion of the stent provides good tackingcharacteristics to prevent stent movement within the artery.Furthermore, the closely spaced cylindrical elements at regularintervals provide uniform support for the wall of the artery, andconsequently are well adapted to tack up and hold in place small flapsor dissections in the wall of the artery, as illustrated in FIGS. 2 and3.

The stent patterns shown in FIGS. 1-3 are for illustration purposes onlyand can vary in size and shape to accommodate different vessels or bodylumens. Further, the stent 10 is of a type that can be used inaccordance with the present invention.

The inverted cylindrical end ring configuration of the present inventionstent can be incorporated into the design of virtually any stent patternand operates to help reduce the stent-to-shoulder distance. Thestent-to-shoulder distance refers to the length that each end of thestent extends relative to the tapered shoulder region of the expandablemember or balloon. The shoulder 28 (FIG. 2) of the balloon 22 istypically tapered in design at each end of the balloon with a balloonworking length 31 formed therebetween. Accordingly, a negativestent-to-shoulder distance is created if the end rings extend beyond theballoon working length and into the balloon tapered shoulder region. Thepresent invention stent benefits from having a negativestent-to-shoulder distance as will be set forth in further detail below.On the other hand, a positive stent-to-shoulder distance is created ifthe stent end rings remain within the balloon working length. This istypically the case of a stent without the inverted end rings of thepresent invention stent.

More specifically, in studies performed on a prototype with invertedcylindrical end rings incorporated therein and based on the design ofthe VISION® stent, manufactured by Advanced Cardiovascular Systems,Inc., of Santa Clara, Calif., it was demonstrated that the stent lengthof 21 mm remained unchanged both before and after expansion of therespective stent. With the expansion of the stent, the invertedcylindrical end rings extend beyond the balloon working length therebycreating a negative stent-to-shoulder distance 29 (FIG. 4) of about −0.3mm. FIG. 4 illustrates the inverted cylindrical end rings of the stentin a fully expanded diameter. In comparative studies performed on aVISION® stent without inverted cylindrical end rings cut to a length of20.2 mm, it was demonstrated that the stent experienced shortening afterexpansion and resulted in a stent length of 19.5 mm, a length change of−0.7 mm. This same stent without inverted cylindrical end rings yieldeda positive stent-to-shoulder distance of about 0.4 mm. FIG. 5illustrates the stent without the inverted cylindrical end rings of thepresent invention stent in an expanded diameter. It is apparent that thecylindrical rings at each stent end of the stent shown in FIG. 5 are notcompletely expanded to the extent of the inverted cylindrical end ringsof the stent shown in FIG. 4. Accordingly, the incorporation of invertedcylindrical end rings into a particular stent design provides the stentwith the ability to effect a complete expansion. Further, theincorporation of inverted cylindrical end rings into a particular stentdesign results in the stent having a pristine deployment and aconsistent stent length after expansion.

In keeping with the present invention, FIGS. 6-15 depict stent 30 invarious configurations. Referring to FIG. 6A, for example, stent 30 isshown in a flattened condition (without the inverted cylindrical endrings of the present invention) so that the pattern can be clearlyviewed, even though the stent is in a cylindrical form in use, such asshown in FIG. 6C. The stent is typically formed from a tubular member,however, it can be formed from a flat sheet such as shown in FIG. 6A androlled into a cylindrical configuration as shown in FIG. 6C. FIG. 6Billustrates a partial plan view of the stent of FIG. 6A expanded toapproximately 3.0 mm inside diameter of the stent.

As shown in FIGS. 6-15, stent 30 is made up of a plurality ofcylindrical rings 40 which extend circumferentially around the stentwhen it is in a tubular form. The stent has a delivery diameter 42 (FIG.7C) and an implanted diameter 44 (FIG. 7B). Each cylindrical ring 40 hasa cylindrical ring proximal end 46 and a cylindrical ring distal end 48.Typically, since the stent is laser cut from a tube there are nodiscreet parts such as the described cylindrical rings and links.However, it is beneficial for identification and reference to variousparts to refer to the cylindrical rings and links and other parts of thestent as follows.

Each cylindrical ring 40 defines a cylindrical plane 50, which is aplane defined by the proximal and distal ends 46, 48 of the ring and thecircumferential extent as the cylindrical ring travels around thecylinder. Each cylindrical ring includes cylindrical outer wall surface52 which defines the outermost surface of the stent, and cylindricalinner wall surface 53 which defines the innermost surface of the stent.Cylindrical plane 50 follows the cylindrical outer wall surface.

With further reference to FIGS. 6-15, undulating link 54 is positionedwithin cylindrical plane 50. The undulating links connect onecylindrical ring 40 to an adjacent cylindrical ring 40 and contribute tothe overall longitudinal flexibility to the stent due to their uniqueconstruction. The flexibility of the undulating links derives in partfrom curved portion 56 connected to straight portions 58 wherein thestraight portions are substantially perpendicular to the longitudinalaxis of the stent. Thus, as the stent is being delivered through atortuous vessel, such as a coronary artery, the curved portions 56 andstraight portions 58 of the undulating links will permit the stent toflex in the longitudinal direction which substantially enhances deliveryof the stent to the target site. The number of bends and straightportions in a link can be increased or decreased from that shown, toachieve differing flexibility constructions. With the straight portionsbeing substantially perpendicular to the stent longitudinal axis, theundulating link acts much like a hinge at the curved portion to provideflexibility. A straight link that is parallel to the stent axistypically is not flexible and does not add to the flexibility of thestent.

Referring to FIGS. 6-11, the stent 30 can be described more particularlyas having a plurality of first peaks 60, second peaks 61, and valleys62. Although the stent is not divided into separate elements, for easeof discussion references to peaks and valleys is appropriate. The numberof peaks and valleys can vary in number for each ring depending upon theapplication. Thus, for example, if the stent is to be implanted in acoronary artery, a lesser number of peaks and valleys are required thanif the stent is implanted in a peripheral artery, which has a largerdiameter than a coronary artery. As can be seen, for example, in FIG.6A, peaks 60, 61 are in phase 63, meaning that the peaks 60, 61 point inthe same direction and are substantially aligned along the longitudinalaxis of the stent. It may be desirable under certain circumstances toposition the peaks so that they are out of phase, that is, the peaks ofone ring would be circumferentially offset from the peaks of an adjacentring so that the apex of adjacent peaks pointed toward each other. Thisout of phase configuration is shown in FIGS. 7-11, and 13-15, withrespect to the configuration of the inverted cylindrical end rings 82and the adjacent cylindrical rings 40. As shown in FIGS. 6-15, the peaksare circumferentially offset 64 from the valleys and from the undulatinglink 54. Positioning the peaks, valleys, and undulating links in thismanner, provides a stent having uniform expansion capabilities, highradial strength, a high degree of flexibility, and sufficient wallcoverage to support the vessel.

It should be appreciated that the stent patterns shown in FIGS. 6-15 arefor illustration purposes only and can vary in shape and size toaccommodate different vessels or body lumens. Thus, rings 40 connectedby links 54 can have any structural shape and are not limited to theaforedescribed undulating rings. Links connecting the rings can alsoinclude oscillating patterns, sinusoidal patterns and zig-zag patterns.

For illustration purposes, one exemplary embodiment of the stent 30 ofthe present invention is shown in FIGS. 7A-7C. In particular, aplurality of inverted cylindrical end rings 82 are coupled at least inpart to a plurality of adjacent cylindrical rings 40 on at least one ofa proximal end 32 and a distal end 34 of the stent. At least oneinverted cylindrical end ring is a mirror image of at least onecorresponding adjacent cylindrical ring such that a symmetricalconfiguration 36 is present on at least one of the proximal end 32 andthe distal end 34 of the stent. The resultant shape of the invertedcylindrical end rings may be dependent on the type of stent design usedfor a particular application. Thus, for example, if the cylindricalrings include U-shaped portions and W-shaped portions, then the invertedcylindrical end rings likewise can “mirror” those respective shapes suchthat complete symmetry exists on at least one of the proximal end andthe distal end of the stent.

In another embodiment shown in FIG. 7D, it is contemplated by theinvention that the plurality of inverted cylindrical end rings 82 canassume a different shape from that of the corresponding plurality ofadjacent cylindrical rings 40 while positioned on at least one of theproximal end 32 and the distal end 34 of the stent. It is furthercontemplated by the present invention that the inverted cylindrical endrings can assume virtually any structural undulating shape.

It is contemplated by the present invention that the symmetricalconfiguration 36 is present on at least one of the proximal end 32 andthe distal end 34 of the stent 30 when the first peaks 60 of theinverted cylindrical end rings 82 and the adjacent cylindrical rings 40are coupled at least in part to each other in the form of a mirrorimage. Similarly, the symmetrical configuration is present on at leastone of the proximal end and the distal end of the stent when the secondpeaks 61 of the inverted cylindrical end rings and the adjacentcylindrical rings are coupled at least in part to each other in the formof a mirror image. The coupling of the first peaks and the second peaksof the inverted cylindrical end rings and the adjacent cylindrical ringsto each other, respectively, occurs by laser cutting a pattern of aparticular stent design into tubing, or a flat sheet, which is thenrolled up in a cylindrical configuration with the longitudinal edgeswelded to form a cylindrical member, as further described below. Theplurality of inverted cylindrical end rings are configured to becompletely expanded at about 95% up to about 100% of the inside diameterof the stent.

In keeping with the invention, and as shown in FIGS. 6-11, each of thecylindrical rings has a plurality of first peaks 60 which have firststruts 66 attached to a first apex 67. The first struts can be eithercurved or straight depending upon the particular application. Thecylindrical rings also have second peaks 61 which have second struts 68attached to a second apex 69. Again, the second struts can be eithercurved or straight depending upon the particular application.Importantly, the length of the second struts 68 is shorter than thelength of the first struts 66. As can be seen in FIGS. 6C, 7C, 8C, and9C, when the stent is in a crimped condition, or a partially crimpedcondition, the first struts and second struts respectively will becloser to each other when the stent is compressed or crimped onto theballoon or expandable member of the catheter. The crimping orcompressing process, however, also moves the undulating link 54 alongwith its curved portion 56 closer to the second peak. In order to allowthe stent to be more tightly crimped onto the balloon portion of thecatheter, and to avoid overlapping between the undulating link and thesecond peak, the second struts 68 are shorter than the first struts 66,thus avoiding any overlapping contact between the curved portion of theundulating link and the second peak. The various stent struts, curvedportions, links, and peaks and valleys may contact each other when thestent is crimped or compressed, but overlapping is an undesirablefeature.

More particularly, in order to more tightly crimp or compress thecylindrical rings 40 of the stent 30, the undulating link 54 is tightlycrimped or compressed into contact with, or near contact with, secondpeak 61. As can be seen, for example, in FIG. 7C, curved portion 56 andstraight portions 58 are in close relation to second peak 61 and areeither in contact (not shown) or near contact with second apex 69. Thecurved portion is proximal to the second peak and the various struts ineach of the rings are tightly compressed to be in contact or nearcontact with each other. For example, first struts 56 and second struts58 as well as arm 76 of the undulating link all are in close contact, orcontact with each other, in order to provide a very low profile, tightlycrimped stent onto the balloon portion of the catheter. Likewise, if thestent is formed of a self-expanding material such as nickel-titanium,the stent will similarly be tightly crimped and positioned within asheath or within the catheter for delivery in the vascular system.Importantly, the curved portion and the straight portions of theundulating link are positioned relative to the second peak to allow thestent to be tightly crimped as described.

Referring to FIGS. 6-11, the stent 30 of the invention also can bedescribed as having cylindrical rings formed of U-shaped portions 70,Y-shaped portions 72, and W-shaped portions 74. Again, while the stentis generally laser cut from a tube and it typically has no discreetparts, for ease of identification the stent of the invention also can bereferred to as having U-, Y-, and W-shaped portions. The U-shapedportions have no supporting structure attached thereto. The Y-shapedportions, at their base, or apex, have arm 76 extending therefrom whichis attached to undulating link 54. The W portion has at its base orcurve portion an arm 78 which attaches at the other end of theundulating link. The length of the arms attaching the links to the ringscan vary.

Due to the intricate patterns as disclosed in FIGS. 6-11, the rate ofexpansion of the various portions of the stent, including the U-shapedportion 70, the Y-shaped portion 72, and the W-shaped portion 74, canvary. Accordingly, one aspect of the invention provides for differentradii of curvature at various points so that the stent will expandevenly and uniformly. Thus, first radius 71 which corresponds with firstpeak 60 has a smaller radius of curvature than second radius 72 whichcorresponds with second peak 61. Generally, the longer the strutsassociated with a peak, the more easily that portion of the stent willexpand, so that a smaller radius is associated with peaks having longerstruts. Likewise, for peaks, such as second peak 61, which has struts 68that are shorter than the struts 66 of first peak 60, a greater radiusof curvature is present which will expand more easily in order tocompensate for the stiffer bending moments created by the shorter struts68.

Also referring to FIGS. 6-11, the radius of curvature of the variousportions of the W-shaped portion also varies to provide uniform stentexpansion. Since the second peak 61 and its associated struts 68 have atendency to expand more slowly as the stent is expanded, a greaterradius of a curvature is provided in the adjacent part of the W-shapedportion 74. Thus, third radius 75 of the W-shaped portion 74 is greaterthan the fourth radius 77 in the W-shaped portion. The third radius 75is adjacent to second peak 61 which has a tendency to expand moreslowly, while fourth radius 77 is adjacent the first peak 60 which has atendency to expand more easily. By varying the radii of curvature in theW-shaped portion, the stent will expand more evenly and compensate forthe varying rates of expansion of adjacent portions in a cylindricalring.

It is also a design feature that more or fewer undulating links 54 willbe positioned between adjacent cylindrical rings 40. Further, in orderto increase stent stability, straight links 80, as shown in FIG. 9A, inaddition to undulating links 54, connect adjacent cylindrical rings. Thestraight links will provide stability and assist in preventing stentforeshortening, as do the undulating links. Further, the straight linksmay provide more rigidity in a localized area, such as at the stentends, such that it may be desirable to incorporate more straight linksbetween the cylindrical rings at the stent ends than in the center ofthe stent. The straight links used in conjunction with the invertedcylindrical end rings 82 of the present invention provide enhanced rigidconnections at both the proximal end 32 and the distal end 34 of thestent.

FIG. 9 is another exemplary embodiment of a particular stent designincorporating the inverted cylindrical end rings 82 of the presentinvention to enhance the mechanical properties of the stent. The stent30 is similar to the other embodiments except that the radius ofcurvature of all of the peaks and valleys are somewhat larger in orderto make it easier to laser cut the stent pattern from a tubular memberor from a flat sheet. As the stent expands, the peak having a greaterradius of curvature will expand more easily than those having a smallerradius of curvature, thus, compensating for the length of the struts inwhich the peaks having shorter struts have a tendency to expand moreslowly than peaks having longer struts and which have moment arms thatbend more easily.

In one aspect of the invention, after stent 30 is implanted in acoronary artery, or other vessel, because of its novel design, thecylindrical rings 40 have the ability to flex radially as the vesselpulsates when blood pumps through it. Likewise, because of the novel andunique design of undulating links 54, as the vessel moves and pulsatesfrom the pumping blood, the stent can flex longitudinally. The radialand longitudinal flexing of the stent reduces the likelihood that thestent will cause injury to the intima of a coronary artery, which alsomay have a tendency to reduce the likelihood of restenosis.

In another aspect of the invention, the stent 30 is formed so that thevarious struts of the cylindrical rings, including the U-shaped portions70, Y-shaped portions 72, W-shaped portions 74, and the undulating links54, all can be formed so that each has a variable thickness along thestent length. For example, the undulating link, and its associated arms76, 78 may be thicker at one end (arm 76) than at the other end of thelink (arm 78). Further, first struts 66 and second struts 68 may vary inthickness (radial thickness) along their length in order to createvariable flexibility in the rings. As shown in FIG. 12, first peak 60has first struts 66 that have radial thick portion 96 in the middle ofthe struts and radial thin portion 98 near the ends of the struts. Asanother example, the rings at for example the proximal end of the stentmay be thicker radially than the rings in the center of the stent. Avariable thickness stent would benefit from being used in conjunctionwith the inverted cylindrical end rings 82 of the present invention toprovide increased rigid connections between the last two rings at boththe proximal end 32 and the distal end 34 of the stent. Further, it iscontemplated by the present invention that select struts of the invertedcylindrical end rings may have a variable thickness while thecylindrical rings and links maintain a standard thickness throughout thelength of the stent. Other combinations of variable thickness struts canbe used on the rings and links within the stent and can be incorporatedinto the other embodiments as desired.

FIGS. 10-11 and 13-14 illustrate alternative stent patterns that may beused in combination with the inverted stent ring 82 configuration of thepresent invention. Regardless of which stent pattern is ultimately usedin a particular application, the present invention contemplates that theinverted cylindrical end rings have the ability to mirror the respectiveshape of the adjacent cylindrical rings such that complete symmetryexists on at least one of the proximal end and the distal end of thestent. This mirror-like arrangement of the inverted cylindrical ringsand corresponding adjacent plurality of cylindrical rings enhances theability of the stent to effect a complete expansion within the bodylumen for subsequent treatment thereto. As mentioned earlier, a similareffect (i.e., complete expansion of stent) is achieved when the invertedcylindrical end rings assume a different shape from that of thecorresponding adjacent cylindrical rings.

In another embodiment of the present invention shown in FIG. 15,therapeutic drugs can be uniformly loaded and distributed throughreservoirs formed in the struts of the inverted cylindrical end rings 82to help prevent restenosis within the peri-stent area of the stent 30.More particularly, the struts of the inverted cylindrical end ringsincorporate micro-channels 86 and/or depots 88 within their structure tohelp retain the therapeutic drug. For illustration purposes, both typesof reservoirs are shown in the embodiment of FIG. 15 while in practiceeither or both may be incorporated into the design of the stent.Additionally, either type of reservoir can be used on other rings withinthe stent and can be incorporated into the other embodiments as desired.

The stent 30 of the present invention can be mounted on a ballooncatheter similar to that shown in the prior art device in FIG. 1. Thestent is tightly compressed or crimped onto the balloon portion of thecatheter and remains tightly crimped onto the balloon during deliverythrough the patient's vascular system. When the balloon is expanded, thestent expands radially outwardly into contact with the body lumen, forexample, a coronary artery. When the balloon portion of the catheter isdeflated, the catheter system is withdrawn from the patient and thestent remains implanted in the artery. Similarly, if the stent of thepresent invention is made from a self-expanding metal alloy, such asnickel-titanium or the like, the stent may be compressed or crimped ontoa catheter and a sheath (not shown) is placed over the stent to hold itin place until the stent is ready to be implanted in the patient. Suchsheaths are well known in the art. Further, such a self-expanding stentmay be compressed or crimped to a delivery diameter and placed within acatheter. Once the stent has been positioned within the artery, it ispushed out of the catheter or the catheter is withdrawn proximally andthe stent held in place until it exits the catheter and self-expandsinto contact with the wall of the artery. Balloon catheters andcatheters for delivering self-expanding stents are well known in theart.

The rings, inverted cylindrical end rings, and the links, may be made ofa suitable biocompatible material such as stainless steel, titanium,tungsten, tantalum, vanadium, cobalt chromium, gold, palladium,platinum, and iradium, as well as high strength thermoplastic polymers.The inverted cylindrical end rings have a strut thickness and widthranging from about 0.0024 inch (0.0610 mm) up to about 0.0034 inch(0.0864 mm). The stent diameters are very small, so the tubing fromwhich they are made also has a small diameter. For PTCA applications,typically the stent has an outer diameter on the order of about 1.65 mm(0.065 inch) in the unexpanded condition, the same outer diameter of thetubing from which it is made, and can be expanded to an outer diameterof 5.08 mm (0.2 inch) or more. The wall thickness of the tubing is about0.076 mm (0.003 inch). In the case of forming the stent fromcobalt-chromium the wall thickness of the tubing may be reduced. Forstents implanted in other body lumens, such as PTA applications, thedimensions of the tubing are correspondingly larger. While it ispreferred that the stents be made from laser cut tubing, those skilledin the art will realize that the stent can be laser cut from a flatsheet and then rolled up in a cylindrical configuration with thelongitudinal edges welded to form a cylindrical member.

The rings may also be made of materials such as superelastic (sometimescalled pseudoelastic) nickel-titanium (NiTi) alloys. In this case therings would be formed full size but deformed (e.g., compressed) to asmaller diameter onto the balloon of the delivery catheter to facilitateintraluminal delivery to a desired intraluminal site. The stress inducedby the deformation transforms the rings from an austenite phase to amartensite phase, and upon release of the force when the stent reachesthe desired intraluminal location, allows the stent to expand due to thetransformation back to the more stable austenite phase. The NiTi alloyrings may be attached to the other rings through welding, bonding andother well known types of attachments.

The stent of the invention also can be coated with a drug or therapeuticagent. The presence of the inverted cylindrical end rings incorporatedinto the design of the stent of the invention enhances delivery oftherapeutic drug to the peri-stent area. Further, it is well known thatthe stent (when both the rings and links are made from metal) mayrequire a primer material coating such as a polymer to provide asubstrate on which a drug or therapeutic agent is coated since somedrugs and therapeutic agents do not readily adhere to a metallicsurface. The drug or therapeutic agent can be combined with a coating orother medium used for controlled release rates of the drug ortherapeutic agent. Representative examples of polymers that can be usedto coat a stent in accordance with the present invention includeethylene vinyl alcohol copolymer (commonly known by the generic nameEVOH or by the trade name EVAL), poly(hydroxyvalerate); poly(L-lacticacid); polycaprolactone; poly(lactide-co-glycolide);poly(hydroxybutyrate); poly(hydroxybutyrate-co-valerate); polydioxanone;polyorthoester; polyanhydride; poly(glycolic acid); poly(D,L-lacticacid); poly(glycolicacid-co-trimethylene carbonate); polyphosphoester;polyphosphoester urethane; poly(amino acids); cyanoacrylates;poly(trimethylene carbonate); poly(iminocarbonate); copoly(ether-esters)(e.g., PEO/PLA); polyalkylene oxalates; polyphosphazenes; biomolecules,such as fibrin, fibrinogen, cellulose, starch, collagen and hyaluronicacid; polyurethanes; silicones; polyesters; polyolefins; polyisobutyleneand ethylene-alphaolefin copolymers; acrylic polymers and copolymers;vinyl halide polymers and copolymers, such as polyvinyl chloride;polyvinyl ethers, such as polyvinyl methyl ether; polyvinylidenehalides, such as polyvinylidene fluoride and polyvinylidene chloride;polyacrylonitrile; polyvinyl ketones; polyvinyl aromatics, such aspolystyrene; polyvinyl esters, such as polyvinyl acetate; copolymers ofvinyl monomers with each other and olefins, such as ethylene-methylmethacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins,and ethylene-vinyl acetate copolymers; polyamides, such as Nylon 66 andpolycaprolactam; alkyd resins; polycarbonates; polyoxymethylenes;polyimides; polyethers; epoxy resins; polyurethanes;polybutylmethacrylate; rayon; rayon-triacetate; poly(glycerol-sebacate);cellulose acetate; cellulose butyrate; cellulose acetate butyrate;cellophane; cellulose nitrate; cellulose propionate; cellulose ethers;and carboxymethyl cellulose.

“Solvent” is a liquid substance or composition that is compatible withthe polymer and is capable of dissolving the polymer at theconcentration desired in the composition. Representative examples ofsolvents include chloroform, acetone, water (buffered saline),dimethylsulfoxide (DMSO), propylene glycol methyl ether (PM),iso-propylalcohol (IPA), n-propylalcohol, methanol, ethanol,tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl acetamide(DMAC), benzene, toluene, xylene, hexane, cyclohexane, heptane, octane,pentane, nonane, decane, decalin, ethyl acetate, butyl acetate, isobutylacetate, isopropyl acetate, butanol, diacetone alcohol, benzyl alcohol,2-butanone, cyclohexanone, dioxane, methylene chloride, carbontetrachloride, tetrachloroethylene, tetrachloro ethane, chlorobenzene,1,1,1-trichloroethane, formamide, hexafluoroisopropanol,1,1,1-trifluoroethanol, and hexamethyl phosphoramide and a combinationthereof. The therapeutic substance contained in the coating can be forinhibiting the activity of vascular smooth muscle cells. Morespecifically, the therapeutic substance can be aimed at inhibitingabnormal or inappropriate migration and/or proliferation of smoothmuscle cells for the inhibition of restenosis. The therapeutic substancecan also include any active agent capable of exerting a therapeutic orprophylactic effect in the practice of the present invention. Forexample, the therapeutic substance can be for enhancing wound healing ina vascular site or improving the structural and elastic properties ofthe vascular site.

Examples of therapeutic agents or drugs that are suitable for use withthe polymeric materials include sirolimus, everolimus, actinomycin D(ActD), taxol, paclitaxel, or derivatives and analogs thereof. Examplesof agents include other antiproliferative substances as well asantineoplastic, antiinflammatory, antiplatelet, anticoagulant,antifibrin, antithrombin, antimitotic, antibiotic, and antioxidantsubstances. Examples of antineoplastics include taxol (paclitaxel anddocetaxel). Further examples of therapeutic drugs or agents that can becombined with the polymeric materials include antiplatelets,anticoagulants, antifibrins, antithrombins, and antiproliferatives.Examples of antiplatelets, anticoagulants, antifibrins, andantithrombins include, but are not limited to, sodium heparin, lowmolecular weight heparin, hirudin, argatroban, forskolin, vapiprost,prostacyclin and prostacyclin analogs, dextran,D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole,glycoprotein IIb/IIIa platelet membrane receptor antagonist, recombinanthirudin, thrombin inhibitor (available from Biogen located in Cambridge,Mass.), and 7E-3B® (an antiplatelet drug from Centocor located inMalvern, Pa.). Examples of antimitotic agents include methotrexate,azathioprine, vincristine, vinblastine, fluorouracil, adriamycin, andmutamycin. Examples of cytostatic or antiproliferative agents includeangiopeptin (a somatostatin analog from Ibsen located in the UnitedKingdom), angiotensin converting enzyme inhibitors such as Captopril®(available from Squibb located in New York, N.Y.), Cilazapril®(available from Hoffman-LaRoche located in Basel, Switzerland), orLisinopril® (available from Merck located in Whitehouse Station, N.J.);calcium channel blockers (such as Nifedipine), colchicine, fibroblastgrowth factor (FGF) antagonists, fish oil (omega 3-fatty acid),histamine antagonists, Lovastatin® (an inhibitor of HMG-CoA reductase, acholesterol lowering drug from Merck), methotrexate, monoclonalantibodies (such as PDGF receptors), nitroprusside, phosphodiesteraseinhibitors, prostaglandin inhibitor (available from GlaxoSmithKlinelocated in United Kingdom), Seramin (a PDGF antagonist), serotoninblockers, steroids, thioprotease inhibitors, triazolopyrimidine (a PDGFantagonist), and nitric oxide. Other therapeutic drugs or agents whichmay be appropriate include alpha-interferon, genetically engineeredepithelial cells, and dexamethasone.

While the foregoing therapeutic agents have been used to prevent ortreat restenosis, they are provided by way of example and are not meantto be limiting, since other therapeutic drugs may be developed which areequally applicable for use with the present invention. The treatment ofdiseases using the above therapeutic agents is known in the art.Furthermore, the calculation of dosages, dosage rates and appropriateduration of treatment are previously known in the art.

The stent of the present invention can be made in many ways. One methodof making the stent is to cut a tubular member, such as stainless steeltubing to remove portions of the tubing in the desired pattern for thestent, leaving relatively untouched the portions of the metallic tubingwhich are to form the stent. In accordance with the invention, it ispreferred to cut the tubing in the desired pattern by means of amachine-controlled laser as is well known in the art.

After laser cutting the stent pattern the stents are preferablyelectrochemically polished in an acidic aqueous solution such as asolution of ELECTRO-GLO#300, sold by ELECTRO-GLO Co., Inc. in Chicago,Ill., which is a mixture of sulfuric acid, carboxylic acids, phosphates,corrosion inhibitors and a biocompatible surface active agent. Otherelectropolishing solutions are well known in the art. The stents may befurther treated if desired, for example, by applying a biocompatiblecoating.

Other methods of forming the stent of the present invention can be used,such as chemical etching, electric discharge machining, laser cutting aflat sheet and rolling it into a cylinder, and the like, all of whichare well known in the art at this time.

The stent of the present invention also can be made from metal alloysother than stainless steel, such as shape memory alloys. Shape memoryalloys are well known and include, but are not limited to,nickel-titanium and nickel/titanium/vanadium. Any of the shape memoryalloys can be formed into a tube and laser cut in order to form thepattern of the stent of the present invention. As is well known, theshape memory alloys of the stent of the present invention can includethe type known as thermoelastic martensitic transformation, or displaystress-induced martensite. These types of alloys are well known in theart and need not be further described here.

Importantly, a stent formed of shape memory alloys, whether thethermoelastic or the stress-induced martensite-type, can be deliveredusing a balloon catheter of the type described herein, or in the case ofstress induced martensite, can be delivered via a catheter without aballoon or a sheath catheter.

While the invention has been illustrated and described herein, in termsof its use as an intravascular stent, it will be apparent to thoseskilled in the art that the stent can be used in other body lumens.Further, particular sizes and dimensions, number of peaks per ring,connection of inverted end rings to end rings, materials used, and thelike have been described herein and are provided as examples only. Othermodifications and improvements may be made without departing from thescope of the invention.

1. A flexible intravascular stent for use in a body lumen, comprising: aplurality of cylindrical rings aligned along a common longitudinal axisand interconnected to form the stent, each cylindrical ring having afirst delivery diameter and a second implanted diameter; eachcylindrical ring having a plurality of first peaks and second peaks,each of the peaks having a height, the second peaks being shorter thanthe first peaks; at least one undulating link attaching each cylindricalring to an adjacent cylindrical ring, the undulating links having acurved portion extending transverse to the stent longitudinal axistoward the second peak, the height of the second peak being sized sothat as the stent is compressed to the first delivery diameter, thecurved portion is positioned proximal to the second peak; wherein aplurality of inverted cylindrical end rings are coupled at least in partto a plurality of adjacent cylindrical rings on at least one of aproximal end and a distal end of the stent, at least one invertedcylindrical end ring being a mirror image of at least one correspondingadjacent cylindrical ring such that a symmetrical configuration ispresent on at least one of the proximal end and the distal end of thestent; wherein the symmetrical configuration is present on at least oneof the proximal end and the distal end of the stent when the first peaksof the inverted cylindrical end rings and the adjacent cylindrical ringsare coupled at least in part to each other in the form of a mirrorimage.
 2. The stent of claim 1, wherein the symmetrical configuration ispresent on at least one of the proximal end and the distal end of thestent when the second peaks of the inverted cylindrical end rings andthe adjacent cylindrical rings are coupled at least in part to eachother in the form of a mirror image.
 3. The stent of claim 1, whereinthe symmetrical configuration is present on both the proximal end andthe distal end of the stent.